This invention relates in general to means for sensing moisture in soil and closing or opening a path of conduction depending upon the amount of moisture in the soil with respect to a threshold level. In particular, this invention relates to moisture sensing switches for controlling sprinkler systems.
The prior art discloses various circuits for controlling watering systems.
U.S. Pat. No. 4,333,490 discloses a circuit for controlling a watering system in response to ambient conditions. It discloses light and humidity sensors which are resistance varying devices, the variations of which are amplified. It also discloses a timer. Note, however, that it does not disclose a ground sensor.
U.S. Pat. No. 2,599,862 discloses a water control system with a ground probe which supposedly measures the resistance of the soil. However, only a single element ground probe is disclosed.
U.S. Pat. No. 2,578,981 presents another electronic control system with a ground probe. This probe, however, comprises two twelve inch copper electrodes spaced apart in the soil. They sense the variation in resistance of the soil due to moisture in the soil.
U.S. Pat. No. 2,611,643 presents another circuit using ground buried electrodes to measure the resistivity of the soil itself.
U.S. Pat. No. 2,674,490 presents a porous cup which measures moisture tension in the soil. The cup and the tube to which it is attached must be filled with water initially in order to operate.
U.S. Pat. No. 3,500,844 shows an above-ground sensor having a mesh through which moisture passes to provide a conducting path between sensing elements.
U.S. Pat. No. 2,989,667 presents a clock circuit which has terminals adapted to be coupled to moisture sensing, resistance varying sensor. This patent, however, does not disclose such a sensor.
U.S. Pat. No. 3,024,372 presents a clock timer circuit which utilizes a ground varied sensor. The sensor is characterized but it is not disclosed in detail.
U.S. Pat. No. 3,915,185 presents the unique packaging scheme for a clock and solenoid valve, but it discloses no ground moisturizing system.
Other advantages and attributes to this invention will be readily discernible upon reading the text hereinafter.